3. g1f3  3... a7a6  4. e2e3  4... b7b5 A much riskier line than the traditional ways of playing the Queen's Gambit Accepted with Nf6-e6-c5. Black's idea is not to end up with an extra pawn, because that is impossible, but to change the pawn structure on the queenside. 5. a2a4 Necessary to recover the pawn.